Cell biology studies have focused on the role of human T-lymphocytic retroviruses (HTLV, HIV) in human T cell malignancies, acquired immunodeficiency syndrome (AIDS) and human herpesvirus-6 (HHV-6). We have identified and purified a growth factor which stimulates the growth of Kaposi's sarcoma (KS) cells in culture. A monoclonal antibody to this growth factor is currently being prepared and biological characterization of the purified growth factor in vitro and in vivo is in progress. An anti-angiogenic drug which inhibits the growth of AIDS-KS cells as well as normal vascular endothelial cells has been identified. Further characterization of this drug is in progress. A new in vivo model for the study of AIDS-KS cells in hairless guinea pigs is currently being developed by transplanting subcutaneously AIDS-KS cells in the backs of hairless guinea pigs. Expression of cytokine receptors on AIDS-KS cells is also being evaluated. A unique monocytoid cell line from a patient with mycosis fungoides has recently been established and characterization of this cell line as well as the possible involvement of an HTLV-I-like retrovirus is being carried out.